Power semiconductor devices, also known as power devices, are known in the art and used as switches or rectifiers in power electronic circuits. In wind turbines power semiconductor devices can be used to connect the generator with the grid. In some wind turbines power converters (comprising semiconductor devices) controls the power flow to the grid.
It is known in the art that power semiconductor device wear out due to mechanical and thermal stress, therefore it is desirable to be able to estimate the end of lifetime or remaining lifetime for a power semiconductor device. This makes it possible, for example, to plan the replacement of the devices before a critical failure.
U.S. Pat. No. 5,877,419 discloses a method for estimating the service life of a power semiconductor component, comprising the steps of subjecting the component to a periodic load change, measuring an electrical parameter P of the component that serves as an indicator for reliability or durability against the number N of load changes, calculating a derivative dP/dN of the electrical parameter P according to the number N of load changes; and comparing the derivative dP/dN with a target value representing a determined service life.
U.S. Pat. No. 5,650,336 disclose a method for predicting the lifetime of a semiconductor device, in which the time from application of an electric stress, including a current and a voltage, onto an element of the semiconductor device until said element becomes unusable, is measured and thereafter the lifetime of the semiconductor device is predicted, with a second electric stress applied, while utilizing a test, in which a first electric stress is applied. This method is destructive and renders the semiconductor device usable. Further, the method applies stress to an element of the semiconductor, such as a gate oxide film, which makes it impossible to predict the end of lifetime for the semiconductor device.